This pilot study tests the feasibility of an emotion regulation training, Manage Emotions to Reduce Aggression (MERA), to decrease aggression in Veterans with posttraumatic stress disorder (PTSD) and improve PTSD treatment outcomes. Background: Aggression is common among Veterans with PTSD and can lead to devastating interpersonal and societal consequences, such as incarceration, family violence, and disruption of treatment-facilitating factors, such as social support. Veterans with PTSD primarily engage in impulsive aggression (emotional, reactive, and uncontrolled) rather than premeditated aggression (deliberate, instrumental, and planned). Emotion dysregulation, or underdeveloped skills in emotional awareness, emotional acceptance, behavioral control, and/or content-appropriate regulation strategies, fully mediates the relationship between PTSD severity and impulsive aggression in Veterans. Additionally, fear of anxiety predicts which Veterans failed to complete PTSD evidence-based psychotherapy. Emotion regulation appears to influence both aggression and treatment outcomes in Veterans with PTSD; thus, this proposed study targets emotion regulation with the goal of reducing impulsive aggression and preparing Veterans for PTSD evidence-based psychotherapy. Research Plan: Our goal is to test the feasibility of an innovative emotion regulation training, MERA, with an open trial of 20 Afghanistan and Iraq Veterans with PTSD and impulsive aggression. MERA is provided in a 3-session condensed time frame to address logistical barriers faced by younger Veterans who have careers, school, and families that compete with treatment time. The training is delivered in a group format and incorporates emotion education, cognitive-behavioral and acceptance-based skills training, and information about what emotional experiences to expect from PTSD treatments. Veterans will complete emotion regulation and aggression measures weekly. The study's feasibility will be examined using Veterans' judgments of MERA, in addition to recruitment (number of referrals versus those who opt-out), enrollment (proportion screened versus enrolled), initiation (attend 1 session), and completion (attend all 3 sessions) rates. MERA's preliminary effectiveness will be estimated with pre- to 1-month post training changes in aggression and emotion regulation. We predict Veterans who complete MERA will have reductions in IA and emotion dysregulation. Finally, rates of PTSD evidence-based psychotherapy initiation (attend 1 session), engagement (attend at least 2 sessions), and completion (therapist indicates termination is appropriate) will be examined 6 months post MERA. We predict Veterans who complete MERA will initiate, engage, and complete PTSD evidence-based psychotherapies at a greater rate than Veterans who do not complete MERA. Significance: This study supports 2 Veterans Affairs missions: reduce aggression and increase PTSD treatment initiation. First, PTSD is one of the most commonly occurring and costly psychiatric conditions among Veterans, and Veterans with PTSD are more likely to engage in aggressive behavior than civilians with PTSD. Reducing aggression is a critical need for Veterans, their families, and society to reduce interpersonal violence, incarceration, and injury. Secondly, there are effective treatments that have been shown to reduce PTSD symptoms, yet few Veterans with PTSD receive PTSD evidence-based psychotherapies. One reason for the low rate of treatment initiation may be that Veterans fear they will not be able to control their emotional responses when they begin treatment. Equipping Veterans with emotion regulation skills and knowledge about PTSD treatments may help them initiate, complete, and benefit from PTSD evidence-based psychotherapies.